The Internet inadvertently undermines the quality of human interaction, allowing destructive emotional impulses freer reign under specific circumstances. The reason is a neural fluke that results in cyber-disinhibition of brain systems that keep our more unruly urges in check. The tech problem: a major disconnect between the ways our brains are wired to connect, and the interface offered in online interactions.

Communication via the Internet can mislead the brain's social systems. The key mechanisms are in the prefrontal cortex; these circuits instantaneously monitor ourselves and the other person during a live interaction, and automatically guide our responses so they are appropriate and smooth. A key mechanism for this involves circuits that ordinarily inhibit impulses for actions that would be rude or simply inappropriate — or outright dangerous.

In order for this regulatory mechanism to operate well, we depend on real-time, ongoing feedback from the other person. The Internet has no means to allow such realtime feedback (other than rarely used two-way audio/video streams). That puts our inhibitory circuitry at a loss — there is no signal to monitor from the other person. This results in disinhibition: impulse unleashed.

Such disinhibition seems state-specific, and typically occurs rarely while people are in positive or neutral emotional states. That's why the Internet works admirably for the vast majority of communication. Rather, this disinhibition becomes far more likely when people feel strong, negative emotions. What fails to be inhibited are the impulses those emotions generate.

This phenomenon has been recognized since the earliest days of the Internet (then the Arpanet, used by a small circle of scientists) as "flaming," the tendency to send abrasive, angry or otherwise emotionally "off" cyber-messages. The hallmark of a flame is that the same person would never say the words in the email to the recipient were they face-to-face. His inhibitory circuits would not allow it — and so the interaction would go more smoothly. He might still communicate the same core information face-to-face, but in a more skillful manner. Offline and in life, people who flame repeatedly tend to become friendless, or get fired (unless they already run the company).

The greatest danger from cyber-disinhibition may be to young people. The prefrontal inhibitory circuitry is among the last part of the brain to become fully mature, doing so sometime in the twenties. During adolescence there is a developmental lag, with teenagers having fragile inhibitory capacities, but fully ripe emotional impulsivity.

Strengthening these inhibitory circuits can be seen as the singular task in neural development of the adolescent years.

One way this teenage neural gap manifests online is "cyber-bullying," which has emerged among girls in their early teens. Cliques of girls post or send cruel, harassing messages to a target girl, who typically is both reduced to tears and socially humiliated. The posts and messages are anonymous, though they become widely known among the target's peers. The anonymity and social distance of the Internet allow an escalation of such petty cruelty to levels that are rarely found in person: face-to-face seeing someone cry typically halts bullying among girls — but that inhibitory signal cannot come via Internet.

A more ominous manifestation of cyber-disinhibition can be seen in the susceptibility of teenagers induced to perform sexual acts in front of webcams for an anonymous adult audience who pay to watch and direct. Apparently hundreds of teenagers have been lured into this corner of child pornography, with an equally large audience of pedophiles. The Internet gives strangers access to children in their own homes, who are tempted to do things online they would never consider in person.

Cyber-bullying was reported last week in my local paper. The Webcam teenage sex circuit was a front-page story in The New York Times two days later.

As with any new technology, the Internet is an experiment in progress. It's time we considered what other such downsides of cyber-disinhibition may be emerging — and looked for a technological fix, if possible. The dangerous thought: the Internet may harbor social perils our inhibitory circuitry was not designed to handle in evolution.